Interest Expense

12 Months Ended

Dec. 31, 2014

Banking and Thrift, Interest [Abstract]

Interest Expense

(10) Interest Expense

Interest expense consists of the following:

	Year ended December 31
	2014		2013		2012
Changes in fair value:
Subordinated notes	$	1,543	$	3,771	$	1,100
Senior convertible notes		11,373		5,588		—
Convertible notes, net of capitalization(1)		37,095		9,337		17,578
Issuance of Series C preferred stock warrants in connection with senior convertible notes		—		10,677		—
Subordinated notes interest, net of capitalization(2)		—		—		822
Amortization of deferred financing costs for subordinated notes		—		—		636
Debt closing costs		47		585		425
Imputed interest on Cabot obligation		—		391		1,018
Other interest		223		250		211
	$	50,281	$	30,599	$	21,790

(1) The charge recognized as a result of the change in the fair value of the Company’s Convertible Notes is presented net of capitalized interest expense of $0.1 million, $0.1 million and $1.9 million for the years ended December 31, 2014, 2013 and 2012, respectively.

(2) Interest expense recognized from the Company’s Subordinated Notes is presented net of capitalized interest expense of $0.0 million, $0.0 million and $0.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Debt closing costs and commitment fees, consisting primarily of legal and related fees, associated with the issuance or modification of the Company’s Subordinated Notes, Senior Convertible Notes, Convertible Notes, and revolving credit facility are amortized over the term of the debt instrument and recorded in interest expense.

Capitalized interest relates primarily to costs associated with the Company’s third production line and significant improvements for the second production line at the East Providence facility.